Skid steer loaders were first invented about 30 years ago to fill a need for a small highly maneuverable vehicle that was capable of carrying an implement mounted on loader arms. Skid steer loaders are typically small vehicles, on the order of 10 to 14 feet long, that rest on four or more wheels, at least two of which being disposed on each side of the vehicle.
In order to turn these vehicles, the wheels on opposing sides of the skid steer loader are driven at different speeds. This causes the faster moving wheels on one side to advance that side over the ground faster than the other side on slower moving wheels. The effect is to turn the vehicle toward the wheels on the slower moving side. Since the wheels are not turnable with respect to the vehicle, the vehicle turns by skidding slightly, hence the name “skid steer loader.” In the extreme case, the wheels on one side of the vehicle can turn in the opposite direction as the wheels on the other side of the vehicle. They can turn in opposite directions at the same speed or at different speeds. When they turn in opposite directions at the same speed, the skid steer loader will rotate in place about a vertical and generally stationary rotational axis.
This ability to change direction by rotating about an axis within the footprint or perimeter of the loader itself was the primary reason why the skid steer loader achieved its great success.
This mode of turning by skidding permits the skid steer vehicle to operate within confined spaces to provide workers within those spaces the added power that a mobile lifting arm or blade can provide.
The skid steer vehicle is used inside buildings that are under construction or are being fabricated. The skid steer vehicle can carry material and tools quite close to an inside work location right to where workers are fabricating the building, making modifications to the building or other related work. Larger vehicles that have lifting and load-carrying abilities, such as bulldozers, backhoes, front wheel loaders and the like do not have the same ability.
Backhoes with their large rear tires and wide stance cannot easily go through doorways or apertures of buildings that are under construction. Furthermore, their stance is typically too wide to pass through the doorways and their height as well is too large, typically on the order of 10–12 feet off the ground—too large to pass through building doorways or wall openings. Backhoes turn by steering their front wheels with respect to their chassis, giving them a typical turning radius of 25–45 feet, still much too large to use conveniently inside a building
Wheel loaders have an extremely wide stance and large bucket, permitting them to carry and move large loads at relatively high speeds over broken ground. Wheel loaders are intended for such locations as road construction sites, rock quarries, steel mills and other outside locations where large capacity, relatively high speed vehicles are beneficial.
Articulated wheel loaders are also constrained by their method of steering: they include two-piece chassis that bend slightly in the middle permitting them to turn in a circle with a radius of about 30–50 feet. This would require an extremely large area in which to turn around, and they would be dangerous in crowded work areas. With a height of about 10–15 feet, they cannot pass through opening or doorways to be used inside buildings to carry tools and supplies and support inside workers.
The only truly practical work-horse for in-building work is the skid steer loader, and it has been used for that purpose for many years. Several of the advantages to skid steer loaders include their low height, typically no more than 8 or 9 feet. This is low enough to permit the vehicle to pass through a doorway under construction or a small breach in a wall of a building under construction.
A further advantage to skid steer vehicles is their narrow width. They are typically less than six feet wide, permitting them to pass though double door ways into commercial buildings under construction. In this manner, they can easily ferry tools and material from larger vehicles and storage areas outside the building into the building itself where they can be delivered to the workers.
A beneficial feature of skid steer vehicles is their ability to turn in place. By turning in place, skid steer vehicles can often avoid backing up at all when inside a building permitting them to maneuver quite carefully through and around work stations, workers, and piles of materials when moving about inside.
Another common feature to skid steer vehicles is their rigid suspension which limits their speed on rough ground. The inherent pitching and rocking causes operator discomfort, loss of vehicle stability, loss of material in the bucket, and potential for catching on to low-hanging obstructions found in buildings under construction, such as beams, electrical wiring, HVAC conduits and the like.
Until recently, skid steer vehicles did not have suspensions for supporting the vehicle. In the last three or four years such suspensions have been developed. The advantage to these suspensions is that they permit the vehicle to go at much greater speeds over broken ground at construction sites. While not rivaling the speed and load-handling capacities of wheel loaders, their added speed makes them more versatile at construction sites. They can now be used for long distance transport of materials and tools over a large construction site. This reduces the need for larger, more expensive vehicles, such as wheel loaders and backhoes. In addition, since they still have the steering by skidding capability and the narrow, short wheelbase, they are still capable of entering into construction sites through open doorways and maneuvering around within constrained spaces.
When a small suspended vehicle like a suspended skid steer loader is loaded and unloaded and when it travels over an irregular surface, the chassis tends to oscillate up and down. In the case of skid steer vehicles the clearance between the chassis and surrounding objects in the building where the skid steer is operated can be significantly reduced. Doorways that were previously passable can interfere with the chassis or other components fixed to and extending therefrom, such as the operator's compartment cage. For example, when the bucket is loaded, the vehicle's suspension compresses and the chassis is lowered toward the ground. This lowers the operator's compartment cage. In this position, lower chassis components are at greater risk of inadvertently hitting the ground or protrusions therefrom. Similarly, when the bucket is unloaded, the chassis raises and upper portions of the chassis and such elements as operator compartment cages may extend upward and interfere with the top of doorways through which the vehicle passes.
In response, operators of a suspended skid steer vehicle must continually gauge the position of the chassis to insure that it will not interfere with its surroundings when the vehicle is loaded or unloaded. This continual checking process, especially when a suspended skid steer vehicle is operated in a confined space such as a building on a construction site, can be difficult. As a result, operators tend to drive slower and approach potential obstructions and restricted spaces at much slower speeds, not just when they initially maneuver around the obstacles, but each and every time they approach them, since the height of the chassis may have changed.
What is needed therefore is some system for locking the chassis suspensions during loading and unloading of the vehicle.
What is also needed is a system that the operator can manually control to insure the chassis is locked when desired and is unlocked when desired.
What is also needed is a system for automatically adjusting chassis height virtually instantly during and after loading and unloading.
What is also needed is a system for automatically maintaining the chassis suspension height to prevent a sudden and unexpected change in height when the chassis suspensions are unlocked.
What is also needed is a system for preventing the chassis from changing height when the skid steer vehicle is loaded and unloaded.
It is an object of this invention to provide one or more of the foregoing features in one or more of the embodiments claimed below.